Wonder of Twins: Types of Twins and Their Development

What a fascinating topic to explore. What exactly are twins and how do they develop? That is an excellent question, and this paper will cover the two most common types of twins that God has put on this earth! In fact, there are several other different types of twins, such as conjoined twins, mirror-image twins, identical twins, fraternal twins, etc. Those are just some different types of twins and there are more! Due to the many different types of twins, this paper will only be covering different aspects of identical and fraternal twins, how they develop, and the differences between the two sets.

Identical twins also called monozygotic (one cell), is the easier set to describe because they are not genetic, meaning they do not run in families. Identical twins are formed when one fertilized egg (ovum) splits into two embryos with exactly the same genetic information. The biological mechanisms that make a single fertilized egg split into two embryos still remain a mystery. These twins may share the same placenta and amniotic sac, or they may have their own. If they share the same placenta, they are more likely to experience complications than twins who have their own. Since they share the same DNA, these twins will share many characteristics. Despite their shared gene set, identical twins are unique individuals, and in reality, even two identical twins are not exactly alike. This is due to slight differences in the environment of the womb, as well as other factors once they are born. Since they are two individual people, they can have similar or very different personalities. So, it is important to not just assume that they are 100% the same because they most likely are not. However, since their appearance is influenced by the environment in the womb, as well as their genes, identical twins can look quite different, even though they are monozygotic (identical) twins. After birth, they may be treated as identical, groomed and dressed the same, and therefore look almost identical.

Fraternal twins, or rather, dizygotic (two-cell) are formed when two eggs (ova) are fertilized by two sperms and produce two genetically unique children, who are still more alike than individual siblings born at different times. Usually, women only release one egg at a time, but fraternal twins can only occur if the mother releases two eggs in one cycle. This is called hyper ovulation. Unlike identical twins who can share their own placenta and amniotic sac, fraternal twins can only have their own individual placentas and sacs. Due to this, fraternal twins are at the lowest risk of all multiple pregnancies. Just as any siblings, fraternal twins share about 50% of their DNA, half from the mother’s egg and a half from the father’s sperm. Fraternal twins can also be of the same or different genders; two boys, two girls, or one boy and one girl. The chances of the embryos resulting in the same or different genders are the same as for any other baby. The reason they can be different genders is because they are two completely different eggs getting fertilized. Now, what are the differences of having fraternal twins and “regular” siblings? For starters, twins are obviously developed at the same time, while siblings are developed in different pregnancies at separate times. Fraternal twins usually have a closer personality than “regular” siblings, but not as close as identical twins. Some fraternal twins can look so similar to each other that they are assumed to be identical, while other sets of fraternal twins can seem the complete opposite of each other, such as having different hair color, eye color, skin tone, body shape, size and etc.! Their personalities vary depending on how similar they are physical, how they are raised, and the relationship between the two.

One last item to discuss regarding fraternal twins is the fact that they do run in families. By meaning that, genetics definitely play a role in having fraternal twins. However, only the mother’s genetics matter, and this is why. As mentioned above, fraternal twins happen when two eggs simultaneously get fertilized instead of just one, and a father’s genes can not make a woman release two eggs. So, a woman’s chance of having twins is best increased by having a mother, a sister, or an aunt (on either the mother’s or the father’s side) who has had fraternal twins. Remember, only fraternal twins are genetic. Also, the other way of women conceives twins is if they are fraternal twins, have already had fraternal twins, or have siblings who are fraternal twins. One interesting fact: a woman who gets pregnant at age 37 is four times more likely to have fraternal twins than at age 18. Even though she will be less likely to conceive at this time because many women’s ovaries are already starting to fail at that age.

Alas, if a man wants to have twins, then he should marry a woman with that description because the father has no influence. Instead, it would be his daughter who inherits that gene. Here is how. Hyperovulation can be a genetic trait. A woman who has the gene for hyper ovulation can pass it down to her daughter, which increases the daughter’s chances of having twins. Since men carry X (female) and Y (male) chromosomes, they too can also pass on the trait for hyper ovulation to their daughters, increasing their daughter’s chance of having twins.

Now knowing some information about identical and fraternal twins just described from above, this last paragraph will be information regarding both types of twins. A question that people often wonder is if twins have the same blood type and fingerprints? Well, the answer is yes and no. Yes, identical twins do have the same blood type, because they share the same genetic information. Fraternal twins, on the other hand, do not necessarily have the same blood type, because they do not have the same genetic information, but they can. As for fingerprinting, neither type of twin have the same fingerprints. They are individuals, just like everyone else. They may have similar fingerprints but never the same. This is because of tiny differences in the womb, resulting in them having their own set of fingerprints. Since identical twins do not have the same fingerprints, that means that identical twins however are not 100% identical!